植茶年龄和施肥类型对茶园N2O和NO排放的影响规律及内在机理研究

The tea tree is one of the most important cash crops in China, and its planting area and production occupy the first place in the world. Furthermore, as the expansion of tea garden and the corresponding increase in the N fertilizer application, exchanges of C and N trace gases between tea ecosystem and atmosphere would be largely influenced by these practices. As reported, tea garden ecosystem has the capacity and potential of carbon sequestration. So far, however, rare investigations regarding the emissions of nitrogen oxides (i.e., N2O and NO) from tea garden have been reported. Hence, this project intends to conduct in situ fiend measurements of N2O and NO emissions as well as the corresponding environmental drivers in the tea gardens with different planting age and fertilization type. The objectives of this study are to (a) characterize the annual dynamics of N2O and NO emissions from different tea garden ecosystems, (b) quantify the annual N2O and NO emissions as well as direct emission factors under the various tea gardens, and (c) clarify the underlying biogeochemical mechanisms and factors regulating the nitrogen oxide emissions from different tea gardens. Such information will be helpful for providing the optimum management regime of tea garden to reduce environmental pollution and improve production efficiency simultaneously. Meanwhile, the results obtained from this project will provide the reliable parameter for accurate estimation of N2O and NO emission in the agricultural sector of China.

茶树是我国重要的经济作物之一，其种植面积和产量均居世界首位。近年来，中国茶园的不断扩张以及施肥量的增加，势必会对茶园-大气碳、氮气体交换强度产生巨大影响。以往研究表明茶园生态系统具有固碳能力及潜力，但有关茶园氮氧化物（N2O和NO）排放特征的研究尚少见报道，尤其是对多种茶园同时进行观测研究。本研究拟通过对不同植茶年龄和施肥类型茶园的N2O和NO排放及其关键影响因子进行长期原位测定，旨在明确不同茶园生态系统的N2O和NO排放年度动态特征及其年际变化，定量不同茶园生态系统氮氧化物的年排放量和排放因子，并阐明导致不同茶园氮氧化物排放量异同的生物地球化学过程与机理。据此，提出科学合理利用和降低环境污染的茶园管理技术模式，并为准确估算我国农业N2O和NO排放量和实施减排措施提供可靠的科学依据。

因地方经济发展和农民增收的需求，中国亚热带地区有大面积的农田被改为茶园。但是，有关茶园温室气体氧化亚氮（N2O）和环境污染气体一氧化氮（NO）排放的研究尚少见报道。本项目在亚热带地区开展了两周年的田间测定，对比研究了水稻田（种植单季稻-冬季休闲，三种处理：无氮肥、尿素150 kg N ha-1 yr-1插秧前一次性施入和同样尿素用量分三次施入）及其改为茶园1年和5年后不同施肥类型（均为三种处理：无氮肥、以450 kg N ha-1 yr-1施用尿素和同样氮量的油菜籽饼肥）的温室气体和NO排放及其关键影响因子。结果显示：.（1）施肥类型的影响：茶园无氮肥处理的N2O和NO背景排放均值分别为4.0和1.6 kg N ha-1 yr-1；施氮肥极大地促进了两种气体的排放，其中施尿素的N2O和NO排放几乎相当，两年平均排放量分别为17.8和18.9 kg N ha-1 yr-1，而施有机肥的N2O排放显著高于NO，二者的两年平均通量分别为30.4和14.7 kg N ha-1 yr-1，表明施有机肥显著削弱了NO排放22%，但却增强了N2O排放71%；茶园施尿素氮肥的N2O和NO 年直接排放系数分别为3.1%和3.8%，施有机肥的相应值分别为5.9%和2.9%，显然，茶园施氮肥所致两种气体的直接排放系数远高于全球农田平均值（约1%）。.（2）植茶年龄的影响：与稻田相比，改后1和5年龄茶园的N2O年直接排放系数从1.05-2.05%分别增加到了2.47-3.65%和2.75-5.80%，NO年直接排放系数从0.033-0.051%分别增加到了2.00-2.83%和2.66-3.99%，表明两种气体的排放有随植茶年龄增长而增加的趋势；通过定量施肥稻田改茶园后的CH4排放由强排放转为弱吸收的量和N2O排放的大幅度增加量，估算出稻田、1和5年龄茶园的CH4+N2O净排放量（以百年CO2当量计）分别为5436-6986，7152-9634和6601-13026 kg CO2-eq ha-1 yr-1，表明稻田改茶园后温室气体排放没有减弱，且随植茶年龄增加有增强趋势。.可见，茶园是大气N2O和NO重要的排放源，且考虑到茶园在全球热带和亚热带地区广泛分布，特别是在我国其种植面积还在继续扩大，在国家N2O和NO气体排放清单编制和国家N2O和NO减排政策制定中，应充分考虑茶园的排放及其控制。